Support structure for holding filter medium

ABSTRACT

A liquid filter element frame ( 7 ) is provided comprising an elongate injection moulded body, conveniently composed of a series of collinear injection moulded units ( 13 ). The frame has a plurality of support ribs ( 14 ) radiating from a central axis thereof and a support collar ( 17 ) encircling the outer edges of the ribs at the operatively upper end. The collar has formed integral therewith a plurality of radially inwardly directed support rails ( 18 ) having inner ends cooperating with the moulded body between adjacent support ribs thereof. Preferably, the collar has a number of inwardly extending support rails equal to the number of radially extending support ribs with the inner edges ( 19 ) of the support rails being received neatly in a corner formed between each pair of adjacent support ribs. The invention also provides a liquid filter including filter elements having such frames.

FIELD OF THE INVENTION

This invention relates to a filter element for a liquid filter of thetype employing a filter medium, such as a fabric bag or sleeve throughwhich liquid is to pass in order to effect filtration, and wherein afiltration aid such as diatomaceous earth is generally used to form alayer on the outside of the filter medium during operation of thefilter. During operation, dirt becomes deposited on the layer offiltration aid, rather than directly on the filter medium.

More particularly, the invention relates to a filter element of the typecomprising a support frame adapted to be covered by a fabric bag orsleeve as well as to a liquid filter including at least one, andgenerally a series of such filter elements.

BACKGROUND TO THE INVENTION

Filters that employ a filter medium, generally in combination with afiltration aid in order to avoid premature blinding of the filter mediumand thereby to extend the cycle time between back washing procedures,generally operate on the principle that when the filter is turned off,the filtration aid and dirt collected thereby fall to the bottom of thecontainer. When the filter is started up again, inlet fluid serves tostir up the filtration aid usually together with at least some dirt fromthe bottom of the filter container so that the filter aid becomes coatedon to the filter medium once more.

One type of filter that has proved to be highly successful is thatdescribed in my issued South African Patents Nos 93/0761 and 2001/2144.This type of filter utilises a series of generally parallel elongatefilter elements that have a plastics injection moulded frame having, incross-section, a number of longitudinally extending ribs radiating froma central axis and the outer edges of which support the fabric sleeve.The construction of the frame is dictated, to some extent, by the tooldesign and, as a consequence, the operatively upper end of each framehas heretofore been fitted with a moulded collar encircling the upperend of the frame and having a flange that serves to support thedownwardly extending filter element in its operative position relativeto a divider plate that supports the filter elements in a generallyvertical orientation.

This construction, whilst being substantially successful, has proved toresult, in some cases, in the possibility of stresses caused by forcesexerted on the filter elements, in particular during start-up, leadingto failure of the frame in the region of its upper end, and inparticular at the collar. This results from the fact that the upper endis the sole support region of the filter element in use.

In addition, if the fabric bag or sleeve is not held adequately tightlyover the upper end of the frame, the fabric of the sleeve can be pushedin, by liquid pressure, to the flow path between the radiating ribs andcollar with a consequent decrease in flow from the interior of therelevant filter element and an accompanying decrease in filtrationefficiency.

OBJECT OF THE INVENTION

It is accordingly an object of this invention to provide a filterelement frame that is adapted to strengthen the support of the frame atits upper end and also, optionally, to diminish the likelihood of thefabric of the bag or sleeve being pushed into the flow path past thecollar edge.

SUMMARY OF THE INVENTION

In accordance with this invention there is provided a liquid filterelement frame comprising an elongate injection moulded body having aplurality of support ribs radiating from a central axis thereof and asupport collar encircling the outer edges of the ribs at the operativelyupper end thereof, the frame being characterised in that the collar hasformed integral therewith a plurality of radially inwardly directedsupport rails having inner ends cooperating with the moulded bodybetween adjacent support ribs thereof.

Further features of the invention provide for the moulded body tocomprise a plurality, typically six, radiating support ribs in whichcase the collar has an equal number of inwardly extending support railsthe inner edges of which are received neatly in a corner formed betweeneach pair of adjacent support ribs; for the support rails to be flat ingeneral construction with a tapered inner edge for neat accommodation inthe corner between an associated pair of support ribs; for the supportrails to extend downwards beyond the operatively lower end of thecollar; for the operatively outer edges of the lower ends of the supportrails to curve inwards towards the centre thereof; and for theoperatively upper end of the collar to have an integral outwardlydirected support flange.

Preferably, the elongate injection moulded body consists of a series ofcollinear injection moulded units each having an integral support ringinterconnecting the outer edges of the support ribs at the operativelylower end thereof and an operatively upper end that, in the case of allbut the uppermost unit, receives the lower edge of the support ring ofthe super-jacent unit. In such a case the operatively uppermost unitreceives the collar of this invention with its integral support railsand support flange at its upper end. The collar is bonded to theuppermost unit by any suitable means such as ultrasonic welding or, moreconveniently, utilizing solvent welding or a suitable adhesive combinedwith a tight fit of the collar on the element.

The invention also provides filter elements including a filter elementframe as defined above as well as a liquid filter including such filterelements.

In order that the invention may be more fully understood one embodimentthereof will now be described with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic sectional elevation of a liquid filter assembly ofthe type in which the expedient of the invention is embodied;

FIG. 2 is a general schematic sectional elevation of one filter elementhaving a frame composed of a series of collinear plastics injectionmoulded units the uppermost one of which is fitted with a collaraccording to the invention;

FIG. 3 is a similar but enlarged exploded view of the operatively upperend of the filter element frame;

FIG. 4 is a similar elevation showing the collar in the installedposition on the uppermost unit and showing also the next unit down;

FIG. 5 is an end view of the collar alone;

FIG. 6 is an end view of an injection moulded frame unit from theoperatively upper end thereof;

FIG. 7 is an end view of the collar in the installed position on theupper end of the associated frame unit; and,

FIG. 8 is a partly sectioned elevation of the operatively lower end of afilter element.

DETAILED DESCRIPTION WITH REFERENCE TO THE DRAWINGS

The type of liquid filter assembly with which this invention isconcerned typically comprises a container (1) of a circular cylindricalshape and having a concave lower end (2) and a correspondingly convexlid (3) removably secured thereto. Towards the upper end of thecontainer is a transverse, generally horizontal, divider plate (4) whichsupports the upper ends of an array of generally vertical elongatefilter elements (5) each of which has a filter medium in the form of afabric sleeve (6) supported on a supporting frame (7) therefor.

Located in the side wall of the container towards the bottom thereof isan inlet (8) fitted with a one way non-return valve (9) and connectedthrough a control valve (10) to an inlet connection (11) for the liquidto be filtered.

The upper end of the container has an outlet (12) for filtered liquidthrough the side wall thereof located above the level of the dividingwall (4).

In use, liquid enters through the inlet (8); passes through the fabricfilter medium of the sleeves; and thence up the filter elements (5);into the upper region of the container (1) on the opposite and thusupper side of the dividing wall (4); and out through the outlet (12). Inthe type of filter under consideration the fabric filter mediumsupports, in the operative condition, a finely subdivided filtration aidthat is typically diatomaceous earth.

At the end of a filtration cycle the diatomaceous earth and the dirtthat has been trapped thereby fall to the bottom of the container andmust be stirred up in a substantially even manner when the filter isnext started up.

It will be understood that the elongate filter elements, being supportedonly at their upper ends, are subjected to certain stresses and strainsparticularly during start-up and that the operatively upper end of theelements must accept the force that is applied to the elements.

The frame (7) is elongate and is made up of a series of collinearinjection moulded units (13) shown most clearly in FIG. 3 and each ofwhich has, in cross-section, six radiating support ribs (14) the outeredges of which support the sleeve (6). The support ribs (14) areinterconnected at their outer edges by a ring (15) at one end, theoperatively lower end thereof, with the ring encircling the ribs andbeing moulded integral therewith. The operatively lower end of thecomposite frame terminates in such a ring (15 a) (see FIG. 8).

As provided by this invention the operatively upper end (16) of theuppermost frame unit (13) is fitted with a collar (17) that hasintegral, equally angularly spaced, inwardly directed support rails(18). The support rails have convergent innermost edges (19) that aremade to fit tightly between the innermost ends of the support ribs (14)so that each support rail is offset angularly by 30 degrees to each ofthe two adjacent support ribs of the injection moulded frame unit. Asshown in FIG. 4, the collar has an internal flange (20) against whichthe upper end of the injection moulded unit abuts in the installedposition.

The support rails extend appreciably below the lower end (21) of thecollar, as indicated by numeral (22), so that a strong mounting for theoperatively upper end of each filter element frame is provided.

The collar also has an integral outwardly directed support flange (17 a)at its upper end.

The collar units are also injection moulded from plastics material andare permanently secured to the upper end of the associated injectionmoulded frame unit by any suitable means such as solvent welding orother bonding agent or, alternatively, by ultrasonic welding. In anyevent the collar unit is made a tight fit onto the end of the injectionmoulded frame unit so that no play is possible between the two parts inthe operative condition.

The filter element frame is finished at the operatively lower endutilizing a disc (23) made of injection moulded plastics material andhaving a rounded edge (24) as shown in FIG. 8 and as more fullydescribed in my granted South African patent No 2000/2145 the disclosureof which is incorporated herein by reference.

It will be understood that the radially extending support rails thatengage the operatively upper end of the support frame of the filterelement form an extremely firm and robust attachment for the frame tothe divider plate and, according to tests conducted the date, the collarof this invention exhibits appreciably superior strength over previousattachment collars used heretofore. Also, the arrangement of the supportrails extending below the lower edge of the collar itself is effectiveto prevent any filter fabric that may be loose from being pushed byliquid under pressure into the flow passages through the collar andthereby at least partially blocking them.

It will be understood that numerous variations may be made to theembodiment of the invention described above without departing from thescope hereof. In particular, it may be found adequate to provide, forexample, only three inwardly directed support rails in the case of sixsupport ribs on the filter element frame unit itself although theremaining three apertures may be subject to drawing filter fabric intothem in the event that it is too loose.

1. A liquid filter element frame for supporting a filter bag on theoutside thereof, comprising an elongate injection molded body having anoperatively upper end and an operatively lower end, a plurality ofsupport ribs radiating from a central axis of the body and terminatingradially at outer edges of the body, and wherein a separately injectionmolded support collar having an upper end and a lower end encircles theouter edges of the ribs at the operatively upper end of the molded body,and wherein further the collar has formed integral therewith a pluralityof radially inwardly directed support rails having inner endscooperating with the molded body between adjacent support ribs thereofand wherein the inner end of each support rail is received neatly in acorner formed between a pair of adjacent support ribs of the body.
 2. Aliquid filter element frame as claimed in claim 1 in which the collarhas a number of inwardly extending support rails equal to the number ofradially extending support ribs with the inner edges of the supportrails being received neatly in a corner formed between each pair ofadjacent support ribs.
 3. A liquid filter element frame as claimed inclaim 1 in which the support rails are flat in general construction witha tapered inner edge for neat accommodation in the corner between anassociated pair of support ribs.
 4. A liquid filter element frame asclaimed in claim 1 in which the support rails extend downwards beyondthe operatively lower end of the collar to form outer edges to lowerends of the support rails.
 5. A liquid filter element frame as claimedin claim 4 in which the outer edges of the lower ends of the supportrails curve inwards towards a center thereof.
 6. A liquid filter elementframe as claimed in claim 1 in which the operatively upper end of thecollar has an integral outwardly directed support flange.
 7. A liquidfilter element frame as claimed in claim 1 in which the elongateinjection molded body consists of a series of collinear injection moldedunits each having an integral support ring interconnecting the outeredges of the support ribs at the operatively lower end thereof and anoperatively upper end that, in the case of all but an uppermost moldedunit, receives a lower edge of the support ring of a super-jacent unit.8. A liquid filter element frame as claimed in claim 7 in which theupper end of the operatively uppermost molded unit receives the collarwith its integral support rails.
 9. A liquid filter element frame asclaimed in claim 1 in which the collar is bonded to the frame by meansselected from ultrasonic welding, solvent welding and adhesive combinedwith a tight fit of the collar on the frame.
 10. A liquid filterincluding filter elements having frames as claimed in claim 1.